Notes On The Magnetic Effect of Electric Current - CBSE Class 7 Science
Magnetic Effect of Electric Current When an electric current flows through a wire, the wire behaves like a magnet. This is known as the magnetic effect of electric current. This was discovered by Hans Christian Oersted. Once, while preparing for a lecture, he noticed that there was a deflection in the needle of a magnetic compass kept near a wire that was connected to a battery. This deflection occurred every time the battery was switched on and off. He realised that a magnetic field is created around a current-carrying wire in a circuit. Electromagnet When electric current flows through a wire wound around an iron bar, the bar behaves like a magnet. This magnet is called an electromagnet. An electromagnet is formed due to the magnetic effect of electric current.  Electromagnets are used in toys, iron industries, electric bells, cranes and Maglev trains. Cranes are used for separating magnetic materials from junk and to lift cars and other heavy objects. Eye doctors use electromagnets to remove tiny pieces of magnetic material that have accidentally fallen in the eye.  Construction of an Electromagnet The components required to create an electromagnet are two pieces of insulated copper wire, a nail, a battery containing two cells, a bulb with a holder, and some paper clips made of iron. The bulb serves as a resistance to the current in the circuit and it prevents the battery from quick discharge. The circuit to make an electromagnet is shown here. When you switch on the current, the paper clips will cling to the nail. This is because the nail becomes an electromagnet. When the battery is disconnected, the nail is no longer an electromagnet. The paper clips will detach from the nail. Construction and Working of an Electric Bell Circuit: An electric bell consists of an iron core, on which is wound a wire as a coil. One end of the coil is connected to one terminal of a battery, and the other end to a steel rod that acts like a spring for the hammer touching the screw contact. The other terminal of the battery is connected to the screw contact with a switch in the middle. Working: Electric current flows through the coil when the switch is ON, and the iron core acts as an electromagnet. The iron core attracts the hammer towards it. The hammer hits the bell and produces a sound. The circuit breaks at the screw contact when the hammer moves towards the iron core. At this point, the iron core ceases to be an electromagnet. The hammer is pulled back to its original position due to the spring action of the steel rod, and then touches the contact again to complete the circuit. The circuit is completed and current flows through the coil again, and the hammer strikes the bell again. The process repeats itself and you hear a ringing sound since the hammer keeps hitting the bell, until the switch is released.

Summary

Magnetic Effect of Electric Current When an electric current flows through a wire, the wire behaves like a magnet. This is known as the magnetic effect of electric current. This was discovered by Hans Christian Oersted. Once, while preparing for a lecture, he noticed that there was a deflection in the needle of a magnetic compass kept near a wire that was connected to a battery. This deflection occurred every time the battery was switched on and off. He realised that a magnetic field is created around a current-carrying wire in a circuit. Electromagnet When electric current flows through a wire wound around an iron bar, the bar behaves like a magnet. This magnet is called an electromagnet. An electromagnet is formed due to the magnetic effect of electric current.  Electromagnets are used in toys, iron industries, electric bells, cranes and Maglev trains. Cranes are used for separating magnetic materials from junk and to lift cars and other heavy objects. Eye doctors use electromagnets to remove tiny pieces of magnetic material that have accidentally fallen in the eye.  Construction of an Electromagnet The components required to create an electromagnet are two pieces of insulated copper wire, a nail, a battery containing two cells, a bulb with a holder, and some paper clips made of iron. The bulb serves as a resistance to the current in the circuit and it prevents the battery from quick discharge. The circuit to make an electromagnet is shown here. When you switch on the current, the paper clips will cling to the nail. This is because the nail becomes an electromagnet. When the battery is disconnected, the nail is no longer an electromagnet. The paper clips will detach from the nail. Construction and Working of an Electric Bell Circuit: An electric bell consists of an iron core, on which is wound a wire as a coil. One end of the coil is connected to one terminal of a battery, and the other end to a steel rod that acts like a spring for the hammer touching the screw contact. The other terminal of the battery is connected to the screw contact with a switch in the middle. Working: Electric current flows through the coil when the switch is ON, and the iron core acts as an electromagnet. The iron core attracts the hammer towards it. The hammer hits the bell and produces a sound. The circuit breaks at the screw contact when the hammer moves towards the iron core. At this point, the iron core ceases to be an electromagnet. The hammer is pulled back to its original position due to the spring action of the steel rod, and then touches the contact again to complete the circuit. The circuit is completed and current flows through the coil again, and the hammer strikes the bell again. The process repeats itself and you hear a ringing sound since the hammer keeps hitting the bell, until the switch is released.

Activities

 Activity 1  Footprints-science.com has created a nice simulation on working of an electric bell. Using this virtual activity we can understand that how an electromagnet is useful in the construction of a n electric bell. Go to Actitivity Activity 2 childrensuniversity.manchester.ac.uk has developed an interactive online simulation which explains how electricity is generated from various sources, using the principle of a generator. In this one gets to build a wind turbine by assembling the components given. An interactive quiz is given at the end to test the understanding of the topic covered. Go to Acivity Activity 3 learnthings.co.za has created an interactive activity which enables one to understand the concept of electricity and magnetism. In this activity one can see the shape of a magnetic field around a single magnet.as well as two magnets. It enables to understand how the fields interact when the poles are repelling or attracting. Also the magnetic field around straight and coiled conductors can be manipulated by changing the direction of the current. Go to Activity

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